Role of ribosomal protein S19-like plasma protein in blood coagulum resorption

Participation of delta annexin A3 in the ribosomal protein S19 C-terminus-dependent inhibitory mechanism of the neutrophil C5a receptor through delta lactoferrin

Although C5a receptor (C5aR) interacting with its agonist C5a promotes acute inflammation during the initiation phase, the roles of the recycling C5aR during the resolution phase are still unclear. We found that C5aR interacted with its antagonist/agonist ribosomal protein S19 (RP S19) polymer or a RP S19 polymer functional analogue S-tagged C5a/RP S19, which connects an RP S19 C-terminus (IAGQVAAANKKH) to the S-tagged C5a C-terminus, promoted acute inflammation at the resolution phase via an activation of the apoptosis-inducing transcription factor delta lactoferrin (δLf) in neutrophils and the membrane mobilizing factor full-length annexin A3 (ANXA3) in macrophages. To confirm the antagonistic system of the recycling C5aR, S-tagged δLf-coupled BrCN-activated Sepharose 4B beads were incubated with cytoplasmic proteins and identified a neutrophil-specific δANXA3 via pull-down experiments. The S-tagged C5a/RP S19-induced agonistic functions in macrophage-like cells that were differentiated from human promyelocytic leukemia HL-60 cells by phorbol-12-myristate-13-acetate were suppressed by δLf and δANXA3 co-overexpression. δANXA3 seems to participate in the antagonistic system of the neutrophil C5aR involving IAGQVAAANKKH and δLf. Most likely, δANXA3 works as antagonist for the recycling C5aR on neutrophils during the resolution phase of acute inflammation.

Erythroblast differentiation at spleen in Q137E mutant ribosomal protein S19 gene knock-in C57BL/6J mice

We recently found that erythroblast-like cells derived from human leukaemia K562 cells express C5a receptor (C5aR) and produce its antagonistic and agonistic ligand ribosomal protein S19 (RP S19) polymer, which is cross-linked between K122 and Q137 by tissue transglutaminases. RP S19 polymer binds to the reciprocal C5aRs on erythroblast-like cells and macrophage-like cells derived from human monocytic THP-1 cells and promotes differentiation into reticulocyte-like cells through enucleation in vitro. To examine the roles of RP S19 polymer in mouse erythropoiesis, we prepared Q137E mutant RP S19 gene knock-in C57BL/6J mice. In contrast to wild-type mice, erythroblast numbers at the preliminary stage (CD71^high/TER119^low) in spleen based on transferrin receptor (CD71) and glycophorin A (TER119) values and erythrocyte numbers in orbital artery bloods were not largely changed in knock-in mice. Conversely, erythroblast numbers at the early stage (CD71^high/TER119^high) were significantly decreased in spleen by knock-in mice. The reduction of early erythroblast numbers in spleen was enhanced by the phenylhydrazine-induced pernicious anemia model knock-in mice and was rescued by a functional analogue of RP S19 dimer S-tagged C5a/RP S19. These data indicated that RP S19 polymer plays the roles in the early erythroblast differentiation of C57BL/6J mouse spleen.

Role of blood ribosomal protein S19 in coagulum resorption: a study using Gln137Glu-ribosomal protein S19 gene knock-in mouse

Sera of human, guinea pig or mouse contain a strong monocyte chemoattractant capacity that is attributed to the ribosomal protein S19 (RP S19) oligomers generated during blood coagulation. In contrast, sera prepared from Gln137Glu-RP S19 gene knock-in mice contained negligible chemoattractant capacity. When coagula that had been pre-formed from the blood of both the wild type and knock-in mice were intraperitoneally inserted into host mice, after 3 days of recovery, the knock-in mouse coagula remained larger than the wild type mouse coagula. The wild type mouse coagula were covered by multiple macrophage layers at the surface and were infiltrated inside by macrophages. Knock-in mouse coagula exhibited less macrophage involvement. When coagula of knock-in mice and coagula of knock-in mice containing C5a/RP S19, an artificial substitute of the RP S19 oligomers, were intraperitoneally inserted as pairs, the C5a/RP S19 containing coagulum was more rapidly absorbed, concomitant with increased macrophage involvement. Finally, when the knock-in mouse and wild type mouse coagula pairs were inserted into mice in which macrophages had been depleted using clodronate liposome, the size difference of recovered coagula was reversed. These results indicate the importance of the RP S19 oligomer-induced macrophage recruitment in coagulum resorption.

The alternative C5a receptor function

When acute inflammatory states are induced by treatment with chemical mediators in C5-deficient mice, neutrophil influxes are commonly decreased. Therefore, the neutrophil C5a receptor (C5aR) is believed to be a member of the pro-inflammatory receptors. However, C5aR deficiency endows mouse neutrophils with increased sensitivity to Pseudomonas aeruginosa. We have demonstrated that C5aR accepts not only C5a but also ribosomal protein S19 (RP S19) oligomers. RP S19 oligomers released from apoptotic cells promote apoptosis or induce dual agonistic and antagonistic effects on the chemotaxis of macrophages and neutrophils in an autocrine or paracrine manner, respectively. We assumed that the function of C5aR in apoptotic cells is almost the same as that in neutrophils infiltrating acute inflammatory lesions. Therefore, we believe that RP S19 oligomers can explain the opposite response of neutrophils in C5aR-deficient mice. In the present study, we found that antihuman RP S19 rabbit IgG cross-reacted with mouse RP S19 monomers and oligomers in plasma and serum, respectively, whereas anti-human C5a rabbit IgG only cross-reacted with mouse RP S19 oligomers in serum. To examine a role of RP S19 oligomers in vivo, we injected carrageenan (50 microg/100 microL) into the thoracic cavities of mice in the simultaneous presence of rabbit IgG and antihuman C5a rabbit IgG (100 microg/100 microL). Before 4 h and after 24 h, we did not observe any inflammatory cues in pleural exudates and lung substances from control mice. However, infiltrating neutrophils were detected in pleural exudates and lung tissues at 4 h after the addition of anti-human RP S19 rabbit IgG. Moreover, anti-human C5a rabbit IgG retards the initiation phase of carrageenan-induced mouse plurality. Many of the neutrophils infiltrating the thoracic cavities of the mice remained annexin V-negative. Neutrophil infiltration into pneumonic lesions became more severe, as alveolar septal destruction and haemorrhage concomitant with increased numbers of neutrophils in the pleural exudates were observed. These in vivo data demonstrate that the neutrophil C5aR acts as a dual pro-inflammatory and pro-apoptosis receptor during the initiation and the resolution phases of acute inflammation, respectively.